1. Field of the Invention
The present invention relates generally to the field of internal combustion engines. More particularly, it concerns methods and apparatuses for using laser ignition to adaptively adjust the position of one or more ignition locations within a combustion chamber during operation of an engine. It also concerns methods and apparatuses for providing multiple ignition locations during a single cycle of engine operation.
2. Description of Related Art
In a usual ignition apparatus for an internal combustion engine, a high voltage is applied to an ignition plug that is fixed on the wall surface of a combustion chamber in order to ignite an air-fuel mixture by spark discharge. In an ignition apparatus of this kind, however, several problems arise. For instance, since the ignition plug is exposed directly to the combustion chamber, carbon attaches to the ignition plug to render the discharge of the ignition plug difficult. Furthermore, due to a heat loss of the electrodes of the ignition plug, a torch or nucleus of flame generated by the discharge is cooled, and vanishes before reaching a flame. Since the ignition occurs on or very near the wall surface of the combustion chamber, the air-fuel mixture is more difficult to ignite than it would be at the center part of the chamber. Even if it is ignited, it takes a considerable time before the flame spreads over the whole space of the combustion chamber. Further, because the ignition occurs on or very near the wall surface, poor mixing often results due to the difficulties associated with burning fuel from the wall surface.
The problems mentioned above are present not only in conventional carburetor-type engines and port injection engines, but also in newer-generation, direct-injection engines, which have come about, in part, due to ever decreasing NOx emissions standards that require leaner air/fuel ratios. Shown in FIG. 1 is a port injection engine 2. Included in this engine are an inlet port 12, inlet valve 4, exhaust port 14, exhaust valve 6, fuel injector 10, spark plug 8, combustion chamber 17, and piston 16. Air enters the combustion chamber 17 from the inlet port 12 via the inlet valve 4 (with exhaust valve 6 closed). This air is pre-mixed with fuel from fuel injector 10 prior to entering the combustion chamber 17 (i.e., the mixture is xe2x80x9cport-injectedxe2x80x9d). The fuel-air mixture is compressed with piston 16 and then ignited by spark plug 8, forcing the piston 16 downwards in what is called a power-stroke. Exhaust gases may then exit the engine through exhaust port 14 via exhaust valve 6 (with inlet valve 4 closed).
Glancing at FIG. 1, it is apparent that the geometry of the system mandates that the fuel gas mixture be directed toward walls of the combustion chamber 17. Thus, ignition via the confined spark plug 8 must overcome the corresponding quenching and poor mixing discussed above.
Shown in FIG. 2 is a direct injection engine 20, which suffers from the same problems discussed above. In fact, the quenching and poor mixing suffered by the port injection engine 2 may be exacerbated in the direct engines due to the need to have a fuel rich mixture near the spark plug and the resulting very tight physical clearances within the combustion chamber. Engine 20 includes an inlet port 12, inlet valve 4, exhaust port 14, exhaust valve 6, fuel injector 10, spark plug 8, combustion chamber 17, and piston 16. Air enters the combustion chamber 17 from the inlet port 12 via the inlet valve 4 (with exhaust valve 6 closed). The fuel is mixed with this air xe2x80x9cdirectlyxe2x80x9d within the combustion chamber 17 (with valves 4 and 6 closed). The gas-fuel mixture is compressed with piston 16 and then ignited by the spark plug 8, forcing the piston 16 downwards in the power-stroke. Exhaust gases may then exit the engine through exhaust port 14 via the exhaust vale 6 (with inlet valve 4 closed).
It is apparent that, in FIG. 2, the fuel injector 10 and spark plug 8 may be even more physically constrained than in FIG. 1. Due to the illustrated geometry, the fuel must be directed toward the spark plug and the walls of the combustion chamber 17. Correspondingly, ignition via the confined spark plug 8 must overcome quenching and poor mixing conditions associated with the cold boundary layer of the walls of combustion chamber 17.
Several attempts have been made to address these and other numerous, well-known problems in the art of internal combustion engines. One of the most common attempts involves controlling the fuel and air flow within an engine. For instance, to address mixing problems, others have used intake air motion to provide tumble or swirl. Shown in FIG. 3, which illustrates a direct injection engine 30, is a piston 16 having a shaped top 19. Top 19, during operation of the engine, creates a fluid flow pattern (both air and fuel) within combustion chamber 17 that generally resembles the curved arrow illustrated in FIG. 3. In particular, fuel and air xe2x80x9ctumblexe2x80x9d within combustion chamber 17, easing, at least to a degree, some of the deleterious effects of quenching and poor mixing.
Other shaped piston tops and arrangements of different components can lead to different fluid flow patterns, as is known in the art. For example, U.S. Pat. No. 5,058,548, which is hereby incorporated by reference in its entirety, involves an arc-shaped offset cavity in the roof of a combustion chamber and an injector for injecting fuel in the form of a cone. Other examples include effecting the following flows: swirling, swishing, and reverse tumbling, to name a few.
Although such methods have exhibited at least a degree of success, room for improvement remains because these methods are still hampered by the fixed, confined location of ignition. Moreover, quenching and poor mixing problems, although reduced, can still remain troublesome. Further, controlling the fuel injection and the in-cylinder air motion in these aerodynamically dominated systems may be very complex because the air motion and injection processes must change significantly as the engine load changes. At light load, for instance, the fuel is injected late in the compression stroke, into the vicinity of the spark plug, which is located very close to the combustion chamber wall. This is accomplished by a combination of fuel jet modifications, surface interactions, and controlled air motion. Conversely, at high load, the fuel is injected very early during the compression stroke, and efforts must be made to completely mix the fuel and air to homogeneous stoichiometric conditions prior to ignition. Such complexities detract from certain advantages these methods may provide.
Another attempted solution to problems discussed herein involves laser ignition rather than ignition by a spark plug. The following representative patents that disclose this, or related, approaches are: U.S. Pat. Nos. 6,053,140; 5,769,621; 5,756,924; 4,852,529; 4,434,753; and 4,416,226, all of which are hereby incorporated by reference in their entirety.
U.S. Pat. No. 6,053,140 discusses an internal combustion engine with externally supplied ignition, where a compressed air-fuel mixture is ignited, at least partially, with the use of at least one laser beam. The laser beam can be introduced into a combustion chamber via at least one optical waveguide and is focused onto an ignition location. The optical waveguide is positioned in a sealing element bounding the combustion chamber, and the sealing element is located in a cutting plane through the combustion chamber and preferably is constituted by a cylinder head gasket.
U.S. Pat. No. 5,769,621 discusses a method of fuel/oxidizer ignition comprising: (a) application of laser light to a material surface which is absorptive to the laser radiation; (b) heating of the material surface with the laser light to produce a high temperature ablation plume which emanates from the heated surface as an intensely hot cloud of vaporized surface material; and (c) contacting the fuel/oxidizer mixture with the hot ablation cloud at or near the surface of the material in order to heat the fuel to a temperature sufficient to initiate fuel ignition.
U.S. Pat. No. 5,756,924 discusses techniques whereby two or more laser light pulses with certain differing temporal lengths and peak pulse powers are employed sequentially to regulate the rate and duration of laser energy delivery to fuel mixtures to improve fuel ignition performance over a wide range of fuel parameters such as fuel/oxidizer ratios, fuel droplet size, number density and velocity within a fuel aerosol, and initial fuel temperatures.
U.S. Pat. No. 4,852,529 discusses an ignition system for internal combustion engines. The ignition system includes a laser energy generator that is arranged to supply laser energy continuously at an energy level less than that needed to initiate combustion with the energy level being spiked in timed sequence and delivered to the combustion chambers of the engine. The system also includes optic means for focussing the pulsed laser energy at predetermined points within the combustion chambers whereby the focussed laser energy is sufficient to ignite any combustible charge within the combustion chambers, the pulsed laser energy being delivered through a purging chamber to the respective combustion chambers with a purging gas being continuously supplied to the purging chamber to prevent combustion gases flowing towards the laser optic means.
U.S. Pat. No. 4,434,753 discusses an ignition apparatus for an internal combustion engine that includes an intake path supplying a mixture of air and fuel into the combustion chamber of the engine, a particle supplying unit having an ejection port opening into the combustion chamber for supplying minute particles of a material which is not the fuel and has a high light absorption factor, and a light source radiating a laser beam through a light focusing unit toward a suitably selected position in the internal space of the combustion chamber. The laser beam strikes the minute particles of high light absorption factor supplied from the particle supplying unit to produce a torch for igniting the air-fuel mixture.
U.S. Pat. No. 4,416,226 discusses a laser ignition apparatus that includes a laser oscillator that generates at least two successive pulse-shaped laser beams during each compression stroke of the engine. A first pulse-shaped laser beam is generated by a Q switching action of the laser oscillator and thus has a high peak output and a second pulse-shaped laser beam is generated without the Q switching action and has a low peak output but a larger pulse duration than the first laser beam. The first and second pulse-shaped laser beams are guided and directed into the combustion chamber of the engine, and the first laser beam of a high energy density causes the breakdown of the air-fuel mixture in the combustion chamber to develop a plasma. The second laser beam further increases the energy of the plasma to ensure the setting fire of the air-fuel mixture.
Although the systems of these patents may each offer their own significant advantages, they, however, suffer from shortcomings as well. For instance, it appears that none of the described systems allows for adaptive positioning, during an engine cycle, of one or more ignition locations. Rather, most of the described systems appear to employ a (single) ignition location that is fixed throughout cycles. These shortcomings, as will be discussed in detail below, do not allow for a great deal of flexibility. In particular, the described systems, like other conventional internal combustion systems, are forced to adjust the gas and/or air flow within the combustion chamber, which can be a very complex undertaking, to address problems and to improve performance. As described in the context of this invention, adaptively adjusting the ignition location during a cycle offers a better solution.
The disclosed invention overcomes problems mentioned above by eliminating the need to control the fuel and air mixing as functions of the engine speed and load; rather the ignition location may be changed using laser radiation and adaptive optics as described below.
The disclosed invention involves incorporation of a laser ignition system in any type of spark-ignition engine, including a direct-injection engine. The laser ignition system includes a pulsed laser of sufficient energy (e.g., 100 mJ/pulse or more in one embodiment) to create a discharge at the focal point of the focused laser beam. The system also includes a window and window holder to allow optical access into the combustion chamber for the laser pulse, and adaptive optics that allow adjustment of the location of the beam focal point within the combustion chamber. The laser ignition system may be combined with an engine configuration in which the fuel is injected directly into the combustion chamber. Several different combustion chamber configurations are possible.
Objectives of the present include, but are not limited to: (a) minimize fuel-wall interactions and (b) simplify the fuel injection and intake air motion control systems by moving the ignition location, rather than the fuel-air mixture and mixing locations, as is required with conventional electric spark discharge systems.
In one respect, the invention is a laser ignition apparatus for an internal combustion engine. It includes a combustion chamber, a laser, and adaptive optics. The combustion chamber defines one or more ignition locations. By xe2x80x9cdefines,xe2x80x9d it is meant that one or more ignition locations are located within the combustion chamber; the exact location(s) within the chamber is determined by the operation of the invention and, more particularly, by the operation of the adaptive optics. The laser is in optical communication with the combustion chamber. The adaptive optics are in optical communication with the combustion chamber and the laser and are configured to adaptively adjust the position of the one or more ignition locations during operation of the engine. As used herein, by xe2x80x9cadaptively adjust,xe2x80x9d it is meant that the position may be adjusted, manually or automatically (by mechanical and/or electronic means) according to one or more operating conditions or parameters of the engine. For instance, the position may be adaptively adjusted to reduce engine knock. Alternatively, the position may adaptively adjusted according to engine load. Alternatively, the position may be adaptively adjusted according to the type of engine (e.g., direct-injection vs. port-injection engine or gasoline vs. natural gas engine). Any number of other operating conditions or parameters exist, as will be understood by one having ordinary skill in the art with the benefit of this disclosure. Any one or combination of those conditions or parameters may be adapted for by the adjustment in ignition location described herein.
In other respects, the internal combustion engine may include a gasoline engine. The internal combustion engine may include a direct injection gasoline engine. The internal combustion engine may include a port injected gasoline engine. The internal combustion engine may include a natural gas engine. The optics may be configured to adaptively adjust the position of the one or more ignition locations as a function of engine speed or load. The optics may be configured to adaptively adjust the position of the one or more ignition locations as a function of engine knock.
In one respect, the invention is a laser ignition apparatus for providing multiple ignition locations during a cycle of an internal combustion engine. The apparatus includes a combustion chamber, a pulsed laser, and adaptive optics. The combustion chamber defines a first and second ignition location. The pulsed laser is in optical communication with the combustion chamber. The adaptive optics are in optical communication with the combustion chamber and the laser, and the optics are configured to direct a first pulse of laser radiation to the first ignition location and a second pulse of laser radiation to the second ignition location during a single cycle of the engine.
In other respects, the adaptive optics may be further configured to adaptively adjust the position of the first or second ignition location during operation of the engine. The optics may be configured to adaptively adjust the position of the first or second ignition location as a function of engine speed or load. The optics may be configured to adaptively adjust the position of the first or second ignition location as a function of engine knock.
In one respect, the invention is a method for laser ignition in an internal combustion engine. Laser radiation is directed to an ignition location within a combustion chamber with adaptive optics. The position of the ignition location is adaptively adjusted during operation of the engine using the adaptive optics.
In other respects, the position of the ignition location may be adjusted as a function of engine speed or load. The position of the ignition location may be adjusted as a function of engine knock. The method may also include directing laser radiation to a combustion chamber window with the adaptive optics to clean the window.
In one respect, the invention is a method for providing multiple ignition locations during a cycle of an internal combustion engine. A first pulse of laser radiation is directed to a first ignition location within a combustion chamber with adaptive optics. A second pulse of laser radiation is directed to a second ignition location within the combustion chamber using the adaptive optics.
In other respects, the position of the first or second ignition location may be adaptively adjusted during operation of the engine using the adaptive optics. The position of the first or second ignition location may be adjusted as a function of engine speed or load. The position of the first or second ignition location may be adjusted as a function of engine knock. The method may also include directing a third pulse of laser radiation to a combustion chamber window with the adaptive optics to clean the window.